Ladson-Billings, G. (1998). Just what is critical race theory and what's it doing in a nice field like education? International Journal of Qualitative Studies in Education, 11(1), 7-24.
 Asghari N. Developing a model to enhance elementary teachers’ ability to foster functional thinking and algebraic reasoning in elementary students. CSTP. 2014; 2 (3) :141-162 [in Persian]
 Kieran, C. (1992). The learning and teaching of school algebra, In D. A. Grouws (Ed.), Handbook of re-search on mathematics teaching and learning. Reston, V A: NCTM.
 Bell, A. (1996). Problem solving approached to alge-bra: Two aspects. In N. Bednarz, C. Kieran, & L. Lee (Eds.), Approaches to algebra: Perspectives for research and teaching (pp. 167-186). Dordrecht: Kluwer.
 Kaput, J. J. (1995). A research base supporting long term algebra reform. In D. T. Owens, M. K. Reed, & G. M. Millsaps (Eds.), Proceedings of the Seventeenth An-nual Meeting of the North American Chapter of the In-ternational Group for the Psychology of Mathematics Education (Vol. 1, pp. 7194). Columbus, OH: ERIC Clearinghouse for Science, Mathematics, and Environ-mental Education.
 Kaput, J. K. (2000).Transforming algebra from an engine of inequity to an engine of mathematical power by “algebrafying” the K-12 curriculum. Dartmouth, MA: National Center for Improving Student Learning and Achievement in Mathematics and Science.
 Sfard, A., & Linchevski, L. (1994). The gains and the pitfalls of reification? The case of algebra. Educational Studies in Mathematics, 26(26), 191–228.
 Küchemann, D. (1981). ‘Algebra’, in K. Hart (ed.), Children Understands of Mathematics: 11–16, Murray, London, pp. 102–119.
 MacGregor, M., & Stacey, K. (1997). Students under-standing of algebraic notation: 11-15. Educational Stud-ies in Mathematics, 33. pp.1–19.
 Philipp, R. A., 1992. The many uses of algebraic variables, Mathematics Teacher, 85, 7, 557–561.
 Stephens, A. C. (2005). Developing students' under-standings of variable, Mathematics teaching in the mid-dle school, 11(2), 96-100
 Wagner, S. (1983).What is these things called varia-bles? Mathematics Teacher, 76, 474478.
 Swan, M. (2000). Making sense of algebra, Mathe-matics Teaching, (171), 16-19
 Van Ameron, B. (2003). Focusing on informal strat-egies when linking arithmetic to early algebra. Educa-tional Studies in Mathematics, 54, 63 - 75.
 Liebenberg, R., Linchevski, L., Oliver, A., & Sasman, M. (1998). Laying the foundation for algebra: develop-ing an understanding of structure, Proceedings of the Fourth Annual Congress of the Association for Mathe-matics Education of South Africa (pp. 276-282). Pieters-burg, South Africa
 Banerjee, R., & Subramaniam, K. (2011) evolution of a teaching approach for beginning algebra. Educa-tional Studies in Mathematics, 80, 351–367.
 Booth, L. R., & Watson, J. (1990). Learning and teaching algebra. The Australian Mathematics Teacher, 46(3), 12 – 14
 Carraher, D. W., Schliemann, A. D., & Schwartz, J. L. (2008). Early algebra is not the same as algebra early. In Algebra in the early grades (pp. 235-272). New York: Lawrence Erlbaum.
 Novotná, J., & Hoch, M. (2008). How structure sense for algebraic expressions or equations is related to structure sense for abstract algebra. Mathematics Education Research Journal, 20(2), 93-104.
 Warren, E. (2003). The role of arithmetic structure in the transition from arithmetic to algebra. Mathematics Education Research Journal, 15, 122-137.
 Kieran, C. (1992). The Learning and Teaching of School Algebra. In D. Grouws (Ed.), Handbook of Research on Mathematics Teaching and Learning (pp. 390-419). New York: Macmillan Publishing Company.
 Welder, R. M. (2012). Improving algebra preparation: Implications from research on student misconceptions and difficulties. School Science and Mathematics 112 (4), 255 – 264.
 Sfard, A. (1994). Reification as the birth of metaphor. For the Learning of Mathematics, 14 (1), 44-55.
 Capraro, M. M., & Joffrion, H. (2006). Algebraic equations: Can middleschool students meaningfully translate from words to mathematical symbols? Reading Psychology, 27, 147-164
 National Council of Teachers of Mathematics. (2000). Principles and Standards for School Mathematics. Reston, VA: NCTM.
 Sfard, A. (1991). On the dual nature of mathemati-cal conceptions: reflections on process and objects as different sides of the same coin. Educational Studies in Mathematics, 1-36.
 Kieran, C. (2007). Learning and teaching algebra at the middle school through college levels. In F. K. Lester (Ed.), Second handbook of research on mathematics teaching and learning (pp. 707–762). Charlotte, NC: In-formation Age.
 Kieran, C. (1996). The changing face of school al-gebra. In C. Alsina, J. Alvarez, B. Hodgson, C. Laborde, & A. Pérez (Eds.), 8th International Congress on Math-ematical Education: Selected lectures (pp. 271-290). Seville, Spain: S.A.E.M. Thales.
 Radford, L. (2001). The historical origins of algebra-ic thinking. In R. Sutherland, T. Rojano, A. Bell, & R. Lins (Eds.), Perspectives on school algebra (pp. 13-36). Dordrecht, the Netherlands: Kluwer Academic.
 Kieran C. (2004). The Core of Algebra: Reflections on its Main Activities. In: Stacey K., Chick H., Kendal M. (Eds) The Future of the Teaching and Learning of Alge-bra The 12thICMI Study. New ICMI Study Series, vol 8. Springer, Dordrecht